Raster scanning is a long-standing display technique in which a beam is scanned across a display screen to impart a display image. Conventionally, an electron beam in a cathode-ray tube is scanned across a phosphor screen, as in standard television sets and computer display monitors. The pixels of an image are rendered sequentially as the electron beam is scanned across the display screen.
Development has since emphasized various pixelated panel displays in which a panel is formed with multiple pixels, as in a liquid crystal cell. The multiple pixels, or significant groups of the multiple pixels, are rendered substantially simultaneously rather than completely sequentially as in a raster display. Various liquid crystal technologies have been developed. Recently an integrated circuit pixelated reflective display has been developed and is called the digital micromirror device, which is available from Texas Instruments Incorporated.
As is known in the art, the digital micromirror device includes an array of micromechanical mirrors that are formed as part of a structure that is manufactured in accordance with integrated circuit manufacturing processes. Each micromechanical mirror corresponds to one pixel in the display. The digital micromirror device imparts display information on light by controllably tipping each of the micromechanical mirrors to control the amount of light that is reflected from the mirror to a display screen.
With the increasing sophistication and cost of pixelated panel displays, interest has returned to raster scanning. But rather than being used within a cathode ray tube, optical displays are being developed to use raster scanning of a light beam over a display screen. The display screen may be reflective, transparent, or translucent, according to the relative positioning of the light source and the viewer or viewers. The light intensity is modulated in coordination with the raster-scanning of the light beam to impart a display image over the surface of the display screen.
In some instances, microelectrical mechanical system (MEMS) actuators have been applied to raster scanning of light to form an optical display. MEMS actuators provide control of very small components that are formed on semiconductor substrates by conventional semiconductor (e.g., CMOS) fabrication processes. MEMS systems and actuators are sometimes referred to as micromachined systems-on-a-chip.
Examples of such actuators are described in U.S. Pat. No. 6,422,011 for Thermal Out-of-Plane Buckle Beam Actuator and US Patent Application Publication No. 2002-0088224 for Resonant Thermal Out-of-Plane Buckle-Beam Actuator, both assigned to Microsoft Corporation. In these examples, one or more MEMS actuators support one or more mirrors that controllably reflect light to form a raster scan on a display screen. The intensity of the light source is modulated and the micromechanical device functions to raster scan the modulated light over the display.
An aspect of the present invention is an appreciation that raster scanning of a display by a relatively small-scale MEMS device can be constrained by structural limitations of the MEMS device, thereby limiting the scope and range of the raster scan pattern. In a pixelated reflective display such as is provided by digital micromirror devices, the limited motion of the micromechanical devices is adequate to impart the modulation of the light intensity of a single pixel.
The present invention includes, therefore, a microelectrical mechanical system (MEMS) optical raster display system. The system includes a microelectrical mechanical system (MEMS) device that supports a reflective surface and tilts it in first and second transverse directions. The reflective surface is positioned to receive modulated light from a light source and to direct reflected light toward an image surface, such as a display screen, in a raster scan pattern. The raster scanning of the light is coordinated with the modulation of the light to form a display image on the display screen.
In one implementation, the system includes multiple modulated light sources that each direct modulated light toward the reflective surface. The light sources are positioned so that the reflective surface reflects modulated light from each light source to a separate region of the display screen, thereby forming plural contiguous, generally non-overlapping, raster scan patterns.
The raster scanning of multiple light beams allows one reflective surface and MEMS device to render a larger display area than could be rendered with only one light beam. As a result, the cost of implementing such an optical raster display is correspondingly reduced.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.